SF: Redefine VsyncId using FTL mixins

...and make it ftl::Incrementable, as libscheduler_test is about to use
that operation (and so should TokenManager::generateTokenForPredictions
once VsyncId is used consistently over int64_t).

Bug: 241285475
Test: Build
Change-Id: I420058ae69e246af62ed7dd8f1478613f86a79de
6 files changed